Joseph C. answered • 09/17/23
B.S. in Chemistry and Biochemistry with Strong Analytical Knowledge
Let's start off with defining what is an isotope. Sometime's due to natural decay or certain reactions an atom may either lose or gain neutrons. As a result the mass of the atom may increase or decrease. The mass of protons and neutron are close to 1 atomic unit (au) each while an electron is about 1/2000 au. Because the mass of an electron is so small we can neglect it when calculating the mass number of an isotope. So we can use the following equation establish some relationships between mass number, number of protons in an isotope (p), and number of neutrons in an isotope (n): mass number = p + n.
So with your problem we can determine the number of protons, neutrons, and electrons using this equation. We know that because the isotope in question has a neutral charge that the number of protons (p) and electrons (e) are the same. We will use the net charge equation (p - e = charge) to prove this. We can rearrange it to get p = e + charge. When the charge is 0 we get p = e.
Now that we have established this we can move onto the mass number equation. According to the periodic table, the Se atom has 34 protons. With this in mind we can rearrange the mass number equation to calculate the number of neutrons: n = mass number - p. Substituting our values we get n = 78 - 34 = 44. So we now know our Se isotope has 44 neutrons, 34 protons, and 34 electrons.
